It is known that many aircraft, in particular civil transport aircraft, are equipped with a collision warning device making it possible to transmit a warning signal when there is a risk of collision of the aircraft with the terrain. With regard to the collision warning device, this can in particular be a TAWS (Terrain Awareness and Warning System) device, in particular of the EGPWS (Enhanced Ground Proximity Warning System) type or of the GCAS (Ground Collision Avoidance System) type.
When such a collision warning device transmits a warning signal, it is generally up to the pilot to take all action, in particular to pilot the aircraft manually in order to avoid a collision with the terrain.
The patent U.S. Pat. No. 4,924,401 proposes a solution having the purpose of automatically avoiding a collision of the aircraft with the terrain. This solution consists in defining a minimum altitude below which the aircraft must not descend and in automatically piloting the aircraft, by means of an automatic pilot, when that minimum altitude is passed through in descent, in such as way as to then automatically instruct the aircraft to climb and thus to prevent any collision with the terrain.
However, this known solution is particularly adapted to the case where the pilot is unconscious whilst the aircraft is in a dive. Because of this it has the disadvantage of acting very late in the aircraft's trajectory and the action on this trajectory of course is greater as it becomes later. Also, applied to a large passenger aircraft for example, this known solution causes an uncomfortable situation, or even a potential danger for the passengers. Moreover, the risk that the action of the trajectory will not protect the aircraft from a collision with the terrain is also high because of this late action.